CATHODE ACTIVE MATERIAL FOR LITHIUM-ION SECONDARY BATTERY

A cathode active material for a lithium-ion secondary battery contains a lithium transition metal composite oxide. The lithium transition metal composite oxide mainly contains a crystal structure belonging to the space group R-3m, and the following relationship is satisfied: “a≤2.876 Å,” where a represents a lattice constant in the a-axis direction of the lithium transition metal composite oxide.